Almost two weeks into December — one of the coldest months of the year — mercury is still lazily hovering over normal to above-normal levels across most parts of Northwest India. The days are clear and sunny, and nights not as cold or foggy for this time of the year.
Not just the urban centres like Delhi, but day temperatures have been settling at least 3-5℃ above normal in most places in Uttarakhand, Himachal Pradesh, Punjab, as well as Haryana with no cold wave just yet. Delhi, where the mercury dropped to as low as 3℃ by December 20 last year, is still resting around 8.4 to 11℃ at night, while it is touching nearly 28 ℃ (4℃ above-normal) during the day.
WHAT’S DELAYING WINTER?
“The winter is certainly warmer than usual this time. But it cannot be precisely said why,” says India Meteorological Department (IMD) Chief Dr M Mohapatra. The weather department had forecasted higher than normal temperatures for North and north-east India in its winter outlook using its multi-model ensemble.
“One of the factors is — the absence of active western disturbances this year in November and December. The weather has been largely dry, and the westerlies (winds) have not been strong enough. That’s why we have not seen any cold waves or particularly strong foggy days yet,” Mohapatra tells News18. “It seems that the frequency and intensity of WDs may be lesser this winter season.”
Western Disturbances are systems that actually signal the arrival of winter for North India. They are basically rainy storms that form in the Mediterranean Sea, travel eastwards and impact the Himalayas – responsible for the snowfall in the hill states, and rains over the north-western region from November to February and subsequent fall in temperatures.
In the absence of rain, the clear cloudless skies further ensure that sunlight directly reaches the earth surface. As the land gets warmer, it radiates more heat into the atmosphere preventing the mercury from plummeting any further.
IS IT UNUSUAL?
A not-so cold December is unusual, but such seasonal variations are common year-to-year. However, what makes it unique is that all this is happening in a La Nina year when India should have ideally seen a much colder winter. La Nina is when the surface waters of the equatorial Pacific Ocean are cooler than usual. The ocean phenomenon is important because it influences India’s weather as well as the monsoon.
“La-Nina ideally brings a colder winter. But it has not happened this year. Except for the southern peninsula and some parts of Central India where the mercury has dipped below-normal, the temperatures have been mostly near-normal for most of North India,” says the IMD DG.
The persistent rise in global temperatures due to climate change is further triggering change in weather patterns. The data shows that minimum temperatures have been showing a rising trend across the country since 1970, especially during the post monsoon and winter season when the change is being prominently felt.
SO, WHEN WILL THE WINTER ACTUALLY SET IN?
The current IMD forecast suggests it may take a little while for the cold days to actually arrive in the plains. Though a feeble western disturbance has impacted the Jammu and Kashmir region on Monday, it is likely to dissipate very soon. “It is just the extreme northern parts of Jammu and Kashmir, higher reaches of Himachal like Kinnaur, Lahaul Spiti, which are getting some snowfall. The rest of the region is fairly dry,” says Surender Paul, head of IMD’s regional centre in Shimla. Both maximum and minimum temperatures have been fairly above-normal by nearly 3℃ over most parts of the hill state.
No significant western disturbance activity or rain spells are expected till the end of this week at least. However, there may be a gradual fall in minimum temperatures by 2-4℃ during the next few days, but strong foggy conditions are unlikely. IMD has not issued any cold day or cold wave warnings for any of the northern states for the week, except for Uttarakhand that may witness cold wave conditions in some places over the next three days.
Overall, the temperatures on average are likely to remain normal to above-normal for most parts of Northwest India during the entire winter season from December to February.
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